Myeloid-Derived Suppressor Cells Are a Major Source of Wnt5A in the Melanoma Microenvironment and Depend on Wnt5A for Full Suppressive Activity

Exosomes as key mediators in immune and cancer cell interactions: insights in melanoma progression and therapy

Exosomes (30-150 nm) are small extracellular vesicles that are secreted by cells into the extracellular environment and are known to mediate cell-to-cell communication. Exosomes contain proteins, lipids, and RNA molecules in relative abundance, capable of modifying the activity of target cells. Melanoma-derived exosomes (MEXs) promote the transfer of oncogenic signals and immunosuppressive factors into immune cells, resulting in a bias of the immune response towards tumor-promoting processes. MEXs could suppress the activation and proliferation of T cells and dendritic cells and induce differentiation of myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). They can induce apoptosis of antigen-specific CD8 + T cells and promote the transfer of tumor antigens, resulting in immune evasion. Specifically, MEXs can shuttle cytokines like interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) to immune cells or express programmed death-ligand 1 (PD-L1 or CD274), creating an immune-suppressive microenvironment that promotes tumorigenesis. Since exosomes preferentially accumulate in melanoma tissues, this targeted delivery could enhance the bioavailability of treatments while limiting side effects. Here, we review the molecular composition of melanoma-derived exosomes, their mechanisms of action, and their potential as therapeutic targets or biomarkers in melanoma. The summarizations of these mechanisms to appropriately influence exosome-mediated interactions could yield new tactics to elicit anti-melanoma immunity or augment the therapeutic effects of current therapies.

Wnt signaling pathways in biology and disease: mechanisms and therapeutic advances

The Wnt signaling pathway is critically involved in orchestrating cellular functions such as proliferation, migration, survival, and cell fate determination during development. Given its pivotal role in cellular communication, aberrant Wnt signaling has been extensively linked to the pathogenesis of various diseases. This review offers an in-depth analysis of the Wnt pathway, detailing its signal transduction mechanisms and principal components. Furthermore, the complex network of interactions between Wnt cascades and other key signaling pathways, such as Notch, Hedgehog, TGF-β, FGF, and NF-κB, is explored. Genetic mutations affecting the Wnt pathway play a pivotal role in disease progression, with particular emphasis on Wnt signaling's involvement in cancer stem cell biology and the tumor microenvironment. Additionally, this review underscores the diverse mechanisms through which Wnt signaling contributes to diseases such as cardiovascular conditions, neurodegenerative disorders, metabolic syndromes, autoimmune diseases, and cancer. Finally, a comprehensive overview of the therapeutic progress targeting Wnt signaling was given, and the latest progress in disease treatment targeting key components of the Wnt signaling pathway was summarized in detail, including Wnt ligands/receptors, β-catenin destruction complexes, and β-catenin/TCF transcription complexes. The development of small molecule inhibitors, monoclonal antibodies, and combination therapy strategies was emphasized, while the current potential therapeutic challenges were summarized. This aims to enhance the current understanding of this key pathway.

EIF2S2 as a prognostic marker and therapeutic target in glioblastoma: insights into its role and downstream mechanisms

Glioblastoma (GBM) the most common and most aggressive primary brain tumor has a five-year survival rate of less than 5%. The onset of GBM is very complicated and has always been the focus of researchers. This study analyzed data from 637 GBM and 20 normal tissues from The Cancer Genome Atlas (TCGA), and patients were categorized into high and low EIF2S2 expression groups. The Overall survival and disease-free survival of GBM patients in low expression of EIF2S2 group were significantly higher than those in high expression of EIF2S2 group (p < 0.001), and the expression level of EIF2S2 was significantly correlated with tumor grade (p < 0.001) and tumor recurrence (p < 0.001). The study designed three different short hairpin RNA (shRNA) sequence vectors, identifying shEIF2S2-1 as the most effective. This vector significantly reduced EIF2S2 expression, cell proliferation, and migration while increasing apoptosis in SHG-44 and U251 cells (p < 0.01). By detecting SHG-44 cells infected with shEIF2S2 vector and shCtrl with human whole gene expression chip, we identified WNT5A that is a downstream target gene of EIF2S2. Interfering with WNT5A and overexpressing EIF2S2 in SHG-44 and U251 cells revealed that EIF2S2 regulates WNT5A expression. This regulation led to an increased apoptosis rate (p < 0.05) and a significant reduction in cell migration (p < 0.05) in both the EIF2S2 overexpression and shWNT5A interference groups, confirming that WNT5A is a downstream regulatory target of EIF2S2. This study revealed the key role of EIF2S2 in GBM and its potential molecular mechanism.

Innate Immune Cells in Melanoma: Implications for Immunotherapy

The innate immune system, composed of neutrophils, basophils, eosinophils, myeloid-derived suppressor cells (MDSCs), macrophages, dendritic cells (DCs), mast cells (MCs), and innate lymphoid cells (ILCs), is the first line of defense. Growing evidence demonstrates the crucial role of innate immunity in tumor initiation and progression. Several studies support the idea that innate immunity, through the release of pro- and/or anti-inflammatory cytokines and tumor growth factors, plays a significant role in the pathogenesis, progression, and prognosis of cutaneous malignant melanoma (MM). Cutaneous melanoma is the most common skin cancer, with an incidence that rapidly increased in recent decades. Melanoma is a highly immunogenic tumor, due to its high mutational burden. The metastatic form retains a high mortality. The advent of immunotherapy revolutionized the therapeutic approach to this tumor and significantly ameliorated the patients' clinical outcome. In this review, we will recapitulate the multiple roles of innate immune cells in melanoma and the related implications for immunotherapy.

Single-cell spatial multiomics reveals tumor microenvironment vulnerabilities in cancer resistance to immunotherapy

Heterogeneous resistance to immunotherapy remains a major challenge in cancer treatment, often leading to disease progression and death. Using CITE-seq and matched 40-plex PhenoCycler tissue imaging, we performed longitudinal multimodal single-cell analysis of tumors from metastatic melanoma patients with innate resistance, acquired resistance, or response to immunotherapy. We established the multimodal integration toolkit to align transcriptomic features, cellular epitopes, and spatial information to provide deeper insights into the tumors. With longitudinal analysis, we identified an "immune-striving" tumor microenvironment marked by peri-tumor lymphoid aggregates and low infiltration of T cells in the tumor and the emergence of MITF+SPARCL1+ and CENPF+ melanoma subclones after therapy. The enrichment of B cell-associated signatures in the molecular composition of lymphoid aggregates was associated with better survival. These findings provide further insights into the establishment of microenvironmental cell interactions and molecular composition of spatial structures that could inform therapeutic intervention.

WNT5A in Cancer: A Pan-Cancer Analysis Revealing Its Diagnostic and Prognostic Biomarker Potential

BACKGROUND AND OBJECTIVE

The wingless-related integration site family (WNT) signaling pathway is critical for tumor progression and development. It is associated with various neoplasms produced by WNT pathway deregulation; WNT5A, a member of the WNT family, has been linked to carcinogenesis, exhibiting either oncogenic or tumor-suppressive effects. The study investigates how the gene affects certain types of cancer. The study aimed to evaluate the potential prognostic significance of WNT5A genes as diagnostic biomarkers for various types of cancer.

METHODOLOGY

We investigated WNT5A gene expression in a pan-cancer analysis using various bioinformatics databases, including GEPIA (Gene Expression Profiling Interactive Analysis), TIMER2 (Tumor Immune Estimation Resource, Version 2), the University of Alabama at Birmingham Cancer Data Analysis Portal UACLAN databases, the Kaplan-Meier (K-M) plotter, cBioPortal, and Gene Set Cancer Analysis (GSCA). We aimed to gain insight into the expression of WNT5A in various tumors and its relationship with immune infiltration, overall survival, and genetic changes. Public datasets validated WNT5A expression in lung squamous cell carcinoma (LUSC) and stomach adenocarcinoma (STAD) samples.

RESULTS

WNT5A pan-cancer analysis was highly expressed in two cancer types, including STAD and LUSC. Additionally, TIMER results showed a positive association of WNT5A with immune cell infiltration in LUSC and STAD. Survival analysis indicated that LUSC cancer exhibits better overall survival, while STAD has lower overall survival levels, which means a poor prognosis in the STAD cancer type. Furthermore, mutation analysis revealed that the WNT5A gene was mutated in 1.4% of cases, with most alterations being deletions followed by amplifications.

CONCLUSIONS

The WNT5A gene's high expression in many malignancies, including LUSC and STAD, suggests it could be used as a diagnostic biomarker. This study shows a relationship between WNT5A expression and immune cell abundance in LUSC and STAD. Our pan-cancer analysis of this gene is the first of its type, and it will inform future research, comprehensive investigation, and wet lab experiments.

Secretome of Cancer-Associated Fibroblasts (CAFs) Influences Drug Sensitivity in Cancer Cells

Resistance is a major problem with effective cancer treatment and the stroma forms a significant portion of the tumor mass but traditional drug screens involve cancer cells alone. Cancer-associated fibroblasts (CAFs) are a major tumor stroma component and its secreted proteins may influence the function of cancer cells. The majority of secretome studies compare different cancer or CAF cell lines exclusively. Here, we present the direct characterization of the secreted protein profiles between CAFs and KRAS mutant-cancer cell lines from colorectal, lung, and pancreatic tissues using multiplexed mass spectrometry. 2573 secreted proteins were annotated, and differential analysis highlighted understudied CAF-enriched secreted proteins, including Wnt family member 5B (WNT5B), in addition to established CAF markers, such as collagens. The functional role of CAF secreted proteins was explored by assessing its effect on the response to 97 anticancer drugs since stromal cells may cause a differing cancer drug response, which may be missed on routine drug screening using cancer cells alone. CAF secreted proteins caused specific effects on each of the cancer cell lines, which highlights the complexity and challenges in cancer treatment and so the importance to consider stromal elements.

Immune Regulation and Immune Therapy in Melanoma: Review with Emphasis on CD155 Signalling

Melanoma is commonly diagnosed in a younger population than most other solid malignancies and, in Australia and most of the world, is the leading cause of skin-cancer-related death. Melanoma is a cancer type with high immunogenicity; thus, immunotherapies are used as first-line treatment for advanced melanoma patients. Although immunotherapies are working well, not all the patients are benefitting from them. A lack of a comprehensive understanding of immune regulation in the melanoma tumour microenvironment is a major challenge of patient stratification. Overexpression of CD155 has been reported as a key factor in melanoma immune regulation for the development of therapy resistance. A more thorough understanding of the actions of current immunotherapy strategies, their effects on immune cell subsets, and the roles that CD155 plays are essential for a rational design of novel targets of anti-cancer immunotherapies. In this review, we comprehensively discuss current anti-melanoma immunotherapy strategies and the immune response contribution of different cell lineages, including tumour endothelial cells, myeloid-derived suppressor cells, cytotoxic T cells, cancer-associated fibroblast, and nature killer cells. Finally, we explore the impact of CD155 and its receptors DNAM-1, TIGIT, and CD96 on immune cells, especially in the context of the melanoma tumour microenvironment and anti-cancer immunotherapies.

Immune escape and metastasis mechanisms in melanoma: breaking down the dichotomy

Melanoma is one of the most lethal neoplasms of the skin. Despite the revolutionary introduction of immune checkpoint inhibitors, metastatic spread, and recurrence remain critical problems in resistant cases. Melanoma employs a multitude of mechanisms to subvert the immune system and successfully metastasize to distant organs. Concerningly, recent research also shows that tumor cells can disseminate early during melanoma progression and enter dormant states, eventually leading to metastases at a future time. Immune escape and metastasis have previously been viewed as separate phenomena; however, accumulating evidence is breaking down this dichotomy. Recent research into the progressive mechanisms of melanoma provides evidence that dedifferentiation similar to classical epithelial to mesenchymal transition (EMT), genes involved in neural crest stem cell maintenance, and hypoxia/acidosis, are important factors simultaneously involved in immune escape and metastasis. The likeness between EMT and early dissemination, and differences, also become apparent in these contexts. Detailed knowledge of the mechanisms behind "dual drivers" simultaneously promoting metastatically inclined and immunosuppressive environments can yield novel strategies effective in disabling multiple facets of melanoma progression. Furthermore, understanding progression through these drivers may provide insight towards novel treatments capable of preventing recurrence arising from dormant dissemination or improving immunotherapy outcomes.

Myeloid-derived suppressor cells in cancer and cancer therapy

Anticancer agents continue to dominate the list of newly approved drugs, approximately half of which are immunotherapies. This trend illustrates the considerable promise of cancer treatments that modulate the immune system. However, the immune system is complex and dynamic, and can have both tumour-suppressive and tumour-promoting effects. Understanding the full range of immune modulation in cancer is crucial to identifying more effective treatment strategies. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that develop in association with chronic inflammation, which is a hallmark of cancer. Indeed, MDSCs accumulate in the tumour microenvironment, where they strongly inhibit anticancer functions of T cells and natural killer cells and exert a variety of other tumour-promoting effects. Emerging evidence indicates that MDSCs also contribute to resistance to cancer treatments, particularly immunotherapies. Conversely, treatment approaches designed to eliminate cancer cells can have important additional effects on MDSC function, which can be either positive or negative. In this Review, we discuss the interplay between MDSCs and various other cell types found in tumours as well as the mechanisms by which MDSCs promote tumour progression. We also discuss the relevance and implications of MDSCs for cancer therapy.

Targeting the Immunoglobulin IGSF9 Enhances Antitumor T-cell Activity and Sensitivity to Anti-PD-1 Immunotherapy

Immune checkpoints modulate the immune response and represent important immunotherapy targets for cancer treatment. However, as many tumors are resistant to current immune checkpoint inhibitors, the discovery of novel immune checkpoints could facilitate the development of additional immunotherapeutic strategies to improve patient responses. Here, we identified increased expression of the adhesion molecule immunoglobulin superfamily member 9 (IGSF9) in tumor cells and tumor-infiltrating immune cells across multiple cancer types. IGSF9 overexpression or knockout in tumor cells did not alter cell proliferation in vitro or tumor growth in immunocompromised mice. Alternatively, IGSF9 deficient tumor cells lost the ability to suppress T-cell proliferation and exhibited reduced growth in immunocompetent mice. Similarly, growth of tumor cells was reduced in IGSF9 knockout syngeneic and humanized mice, accompanied by increased tumor-infiltrating T cells. Mechanistically, the extracellular domain (ECD) of IGSF9 bound to T cells and inhibited their proliferation and activation, and the tumor-promoting effect of IGSF9 ECD was reversed by CD3+ T-cell depletion. Anti-IGSF9 antibody treatment inhibited tumor growth and enhanced the antitumor efficacy of anti-programmed cell death protein 1 immunotherapy. Single-cell RNA sequencing revealed tumor microenvironment remodeling from tumor promoting to tumor suppressive following anti-IGSF9 treatment. Together, these results indicate that IGSF9 promotes tumor immune evasion and is a candidate immune checkpoint target.

SIGNIFICANCE

IGSF9 is an immune checkpoint regulator that suppresses T-cell activation in cancer and can be targeted to stimulate antitumor immunity and inhibit tumor growth.

Chronic adrenergic stress and generation of myeloid-derived suppressor cells: Implications for cancer immunotherapy in dogs

Recent studies have highlighted a key role played by the sympathetic nervous system (SNS) and adrenergic stress in mediating immune suppression associated with chronic inflammation in cancer and other diseases. The connection between chronic SNS activation, adrenergic stress and immune suppression is linked in part to the ability of catecholamines to stimulate the bone marrow release and differentiation of myeloid-derived suppressor cells (MDSC). Rodent model studies have revealed an important role for β-adrenergic receptor signalling in suppression of cancer immunity in mice subjected to chronic stresses, including thermal stress. Importantly, therapeutic blockade of beta-adrenergic responses by drugs such as propranolol can partially reverse the generation and differentiation of MDSC, and partly restore tumour immunity. Clinical trials in both humans and dogs with cancer have demonstrated that propranolol blockade can improve responses to radiation therapy, cancer vaccines and immune checkpoint inhibitors. Thus, the SNS stress response has become an important new target to relieve immune suppression in cancer and other chronic inflammatory conditions.

WNT5A in tumor development and progression: A comprehensive review

The investigation of tumor microenvironment (TME) is essential to better characterize the complex cellular crosstalk and to identify important immunological phenotypes and biomarkers. The niche is a crucial contributor to neoplasm initiation, maintenance and progression. Therefore, a deeper analysis of tumor surroundings could improve cancer diagnosis, prognosis and assertive treatment. Thus, the WNT family exerts a critical action in tumorigenesis of different types of neoplasms due to dysregulations in the TME. WNT5A, an evolutionary WNT member, is involved in several cellular and physiopathological processes, in addition to tissue homeostasis. The WNT5A protein exerts paradoxical effects while acting as both an oncogene or tumor suppressor by regulating several non-canonical signaling pathways, and consequently interfering in cell growth, cytoskeletal remodeling, migration and invasiveness. This review focuses on a thorough characterization of the role of WNT5A in neoplastic transformation and progression, which may help to understand the prognostic potentiality of WNT5A and its features as a therapeutic target in several cancers. Additionally, we herein summarized novel findings on the mechanisms by which WNT5A might favor tumorigenesis or suppression of cancer progression and discussed the recently developed treatment strategies using WNT5A as a protagonist.

Tumor-derived exosomes: the emerging orchestrators in melanoma

Cutaneous melanoma is an aggressive cancer type derived from melanocytes and its incidence has rapidly increased worldwide. Despite the vast improvement in therapy, melanoma is still confronted with high invasion, metastasis, and recurrence rate. Recent studies have confirmed that the exosomes are naturally occurring membranous extracellular vesicles with nano-sized lipid bilayers, performing as information messagers within cellular reciprocal action. Exosomes are unquestionably endowed with multifaceted roles in various diseases, including melanoma. Notably, tumor-derived exosomes play a pivotal role in conditioning the tumor microenvironment to promote the growth, metastasis, immune escape, and even drug-resistance of melanoma by transferring carcinogenic nucleic acids and proteins. Clinically, the dynamic expressions of exosomal components and loadings in melanoma patients with different tumor stages confer the clinical application of melanoma exosomes as diagnostic biomarkers. Hence, this review highlights the recent complicated roles and mechanisms of melanoma exosomes, as well as their potential as diagnostic and therapeutic targets in melanoma. The in-depth insights into the properties and behaviors of melanoma exosomes are of great potential to yield attractive therapeutic methods for melanoma.

The value of WNT5A as prognostic and immunological biomarker in pan-cancer

Background

Finding new immune-related biomarkers is one of the promising research directions for tumor immunotherapy. The WNT5A gene could stimulate the WNT pathway and regulate the progression of various tumors. Recent studies have partially revealed the relationship between WNT5A and tumor immunity, but the correlation and underlying mechanisms in pan-cancer remain obscure. Thus, we conducted this study aiming to characterize the prognostic value and immunological portrait of WNT5A in cancer.

Methods

The data obtained from The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Cancer Cell Line Encyclopedia (CCLE) databases was utilized to analyze WNT5A expression levels by Kruskal-Wallis test and correlation to prognosis by Cox regression test and Kaplan-Meier test, while the data was also used to study the association between WNT5A expression and immune microenvironment, immune neoantigens, immune checkpoints, tumor mutational burden (TMB), and microsatellite instability (MSI) in pan-cancer. Gene set enrichment analysis (GSEA) was used to clarify the relevant signaling pathways. The R package was used for data analysis and to create the plots.

Results

The pan-cancer analysis revealed that the expression level of WNT5A is generally elevated in most tumors (19/34, 55.88%), and high WNT5A expression was correlated with poor prognosis in esophageal carcinoma (ESCA, P<0.05), low-grade glioma (LGG, P<0.01), adrenocortical carcinoma (ACC, P<0.01), pancreatic adenocarcinoma (PAAD, P<0.01), and head and neck squamous cell carcinoma (HNSC, P<0.05). In addition, WNT5A expression was positively associated with immune infiltration, stromal score, and immune checkpoints in most cancers, and correlated to immune neoantigens, TMB, and MSI. Finally, GSEA indicated that WNT5A is implicated in the transforming growth factor β (TGFβ), Notch, and Hedgehog signaling pathways, which may be related to tumor immunity.

Conclusions

The expression of WNT5A is elevated in most tumors and associated with tumor prognosis. Furthermore, WNT5A is associated with tumor immunity and may be an immunological biomarker in cancer.

Signal pathways of melanoma and targeted therapy

Melanoma is the most lethal skin cancer that originates from the malignant transformation of melanocytes. Although melanoma has long been regarded as a cancerous malignancy with few therapeutic options, increased biological understanding and unprecedented innovations in therapies targeting mutated driver genes and immune checkpoints have substantially improved the prognosis of patients. However, the low response rate and inevitable occurrence of resistance to currently available targeted therapies have posed the obstacle in the path of melanoma management to obtain further amelioration. Therefore, it is necessary to understand the mechanisms underlying melanoma pathogenesis more comprehensively, which might lead to more substantial progress in therapeutic approaches and expand clinical options for melanoma therapy. In this review, we firstly make a brief introduction to melanoma epidemiology, clinical subtypes, risk factors, and current therapies. Then, the signal pathways orchestrating melanoma pathogenesis, including genetic mutations, key transcriptional regulators, epigenetic dysregulations, metabolic reprogramming, crucial metastasis-related signals, tumor-promoting inflammatory pathways, and pro-angiogenic factors, have been systemically reviewed and discussed. Subsequently, we outline current progresses in therapies targeting mutated driver genes and immune checkpoints, as well as the mechanisms underlying the treatment resistance. Finally, the prospects and challenges in the development of melanoma therapy, especially immunotherapy and related ongoing clinical trials, are summarized and discussed.

HIF2 Regulates Intestinal Wnt5a Expression

Radiation therapy for abdominal tumors is challenging because the small intestine is exquisitely radiosensitive. Unfortunately, there are no FDA-approved therapies to prevent or mitigate GI radiotoxicity. The EGLN protein family are oxygen sensors that regulate cell survival and metabolism through the degradation of hypoxia-inducible factors (HIFs). Our group has previously shown that stabilization of HIF2 through genetic deletion or pharmacologic inhibition of the EGLNs mitigates and protects against GI radiotoxicity in mice by improving intestinal crypt stem cell survival. Here we aimed to elucidate the molecular mechanisms by which HIF2 confers GI radioprotection. We developed duodenal organoids from mice, transiently overexpressed non-degradable HIF2, and performed bulk RNA sequencing. Interestingly, HIF2 upregulated known radiation modulators and genes involved in GI homeostasis, including Wnt5a. Non-canonical Wnt5a signaling has been shown by other groups to improve intestinal crypt regeneration in response to injury. Here we show that HIF2 drives Wnt5a expression in multiple duodenal organoid models. Luciferase reporter assays performed in human cells showed that HIF2 directly activates the WNT5A promoter via a hypoxia response element. We then evaluated crypt regeneration using spheroid formation assays. Duodenal organoids that were pre-treated with recombinant Wnt5a had a higher cryptogenic capacity after irradiation, compared to vehicle-treated organoids. Conversely, we found that Wnt5a knockout decreased the cryptogenic potential of intestinal stem cells following irradiation. Treatment with recombinant Wnt5a prior to irradiation rescued the cryptogenic capacity of Wnt5a knockout organoids, indicating that Wnt5a is necessary and sufficient for duodenal radioprotection. Taken together, our results suggest that HIF2 radioprotects the GI tract by inducing Wnt5a expression.

The Metabolic Control of Myeloid Cells in the Tumor Microenvironment

Myeloid cells are a key determinant of tumor progression and patient outcomes in a range of cancers and are therefore being actively pursued as targets of new immunotherapies. The recent use of high-dimensional single-cell approaches, e.g., mass cytometry and single-cell RNA-sequencing (scRNA-seq) has reinforced the predominance of myeloid cells in the tumor microenvironment and uncovered their phenotypic diversity in different cancers. The cancerous metabolic environment has emerged as a critical modulator of myeloid cell functions in anti-tumor immunity versus immune suppression and immune evasion. Here, we discuss mechanisms of immune-metabolic crosstalk in tumorigenesis, with a particular focus on the tumor-associated myeloid cell’s metabolic programs. We highlight the impact of several metabolic pathways on the pro-tumoral functions of tumor-associated macrophages and myeloid-derived suppressor cells and discuss the potential myeloid cell metabolic checkpoints for cancer immunotherapy, either as monotherapies or in combination with other immunotherapies.

High-Dimensional Single-Cell Transcriptomics in Melanoma and Cancer Immunotherapy

Recent advances in single-cell transcriptomics have greatly improved knowledge of complex transcriptional programs, rapidly expanding our knowledge of cellular phenotypes and functions within the tumour microenvironment and immune system. Several new single-cell technologies have been developed over recent years that have enabled expanded understanding of the mechanistic cells and biological pathways targeted by immunotherapies such as immune checkpoint inhibitors, which are now routinely used in patient management with high-risk early-stage or advanced melanoma. These technologies have method-specific strengths, weaknesses and capabilities which need to be considered when utilising them to answer translational research questions. Here, we provide guidance for the implementation of single-cell transcriptomic analysis platforms by reviewing the currently available experimental and analysis workflows. We then highlight the use of these technologies to dissect the tumour microenvironment in the context of cancer patients treated with immunotherapy. The strategic use of single-cell analytics in clinical settings are discussed and potential future opportunities are explored with a focus on their use to rationalise the design of novel immunotherapeutic drug therapies that will ultimately lead to improved cancer patient outcomes.

Melanoma Plasticity: Promoter of Metastasis and Resistance to Therapy

Melanoma is the deadliest form of skin cancer. Although targeted therapies and immunotherapies have revolutionized the treatment of metastatic melanoma, most patients are not cured. Therapy resistance remains a significant clinical challenge. Melanoma comprises phenotypically distinct subpopulations of cells, exhibiting distinct gene signatures leading to tumor heterogeneity and favoring therapeutic resistance. Cellular plasticity in melanoma is referred to as phenotype switching. Regardless of their genomic classification, melanomas switch from a proliferative and differentiated phenotype to an invasive, dedifferentiated and often therapy-resistant state. In this review we discuss potential mechanisms underpinning melanoma phenotype switching, how this cellular plasticity contributes to resistance to both targeted therapies and immunotherapies. Finally, we highlight novel strategies to target plasticity and their potential clinical impact in melanoma.